Silicone elastomer-forming compositions which are capable of curing to elastomers at normal ambient temperatures are now well known in the art. Such compositions are available as two types. One type comprises compositions which are supplied in a single package and which cure on exposure to the moisture in the atmosphere. The other type is supplied as a two package (or two part) composition which cures when the contents of the two packages are mixed in the appropriate proportions. Typically one package of the latter type of composition contains a hydroxyl-terminated polydiorganosiloxane and one or more fillers. The other package contains a silane or siloxane having on average more than two silicon-bonded alkoxy or alkoxyalkoxy groups per molecule and a curing catalyst. Other additives e.g. additional fillers, plasticisers and pigments may be present in either or both packages. Such two-package compositions are described in, for example, British Pat. Nos. 841 825, 844 128, 867 511 and 938 399.
For certain applications of the two part compositions it is often desired to improve the adhesion of the cured elastomer to a substrate, for example glass, aluminium or concrete. It is known that an improvement in adhesion can be realised by incorporating in the composition a silane or siloxane having amino-substituted organic groups in the molecule. One such adhesion promoter is aminopropyltriethoxysilane. Another known adhesion promoter for the two part compositions is glycidoxypropyltrimethoxysilane. Although both silanes provide good adhesion to a wide range of substrates it has been found that the adhesive bond degrades rapidly under wet conditions.